// 根据 byte [] 建立一个 Element 对象
// parameter:
// bytes [out] 返回本次用掉的 byte 数
public static Element Parse(byte[] data,
int start,
out int bytes)
{
bytes = 0;
if (start >= data.Length)
{
throw new ArgumentException($"start 值 {start} 不应越过 data length {data.Length}");
}
int offset = start;
Element element = new Element();
if (data.Length - offset < 1)
{
throw new Exception($"data 长度不足，从 {offset} 开始应至少为 1 bytes");
}
element._precursor = new Precursor(data[offset]);
offset++;
// OID 为 1-14, 元素存储结构为 Precursor + Length of data + Compacted data
if (element._precursor.ObjectIdentifier <= 14)
{
element.OID = element._precursor.ObjectIdentifier;
}
else
{
// OID 为 15-127。元素存储结构为 Precursor + Relative-OID 15 to 127 + Length of data + Compacted data
if (data.Length - offset < 3)
{
throw new Exception($"data 长度不足，从 {offset} 开始应至少为 3 bytes");
}
element.OID = 15 + data[offset];
offset++;
}
if (data.Length - offset < 2)
{
throw new Exception($"data 长度不足，从 {offset} 开始应至少为 2 bytes");
}
if (element._precursor.Offset == true)
{
// 填充字节数
element._paddings = data[offset];
offset++;
}
element._lengthOfData = data[offset];
offset++;
if (data.Length - offset < element._lengthOfData)
{
throw new Exception($"data 长度不足，从 {offset} 开始应至少为 {element._lengthOfData} bytes");
}
element._compactedData = new byte[element._lengthOfData];
Array.Copy(data, offset, element._compactedData, 0, element._lengthOfData);
bytes = offset - start + element._lengthOfData + element._paddings;
// 解析出 Text
if (element._precursor.CompactionCode == (int)CompactionScheme.ApplicationDefined)
{
if (element.OID == (int)ElementOID.OwnerInstitution ||
element.OID == (int)ElementOID.IllBorrowingInstitution
)
{
element.Text = Compress.IsilExtract(element._compactedData);
}
else
{
// 只能用 Content 表示
element.Content = element._compactedData;
// TODO: 此时 Text 里面放什么？是否要让 get Text 抛出异常引起注意?
}
}
else
{
if (element._precursor.CompactionCode == (int)CompactionScheme.Integer)
{
element.Text = Compress.IntegerExtract(element._compactedData);
}
else if (element._precursor.CompactionCode == (int)CompactionScheme.Integer)
{
element.Text = Compress.IntegerExtract(element._compactedData);
}
else if (element._precursor.CompactionCode == (int)CompactionScheme.Numeric)
{
element.Text = Compress.NumericExtract(element._compactedData);
}
else if (element._precursor.CompactionCode == (int)CompactionScheme.FivebitCode)
{
element.Text = Compress.Bit5Extract(element._compactedData);
}
else if (element._precursor.CompactionCode == (int)CompactionScheme.SixBitCode)
{
element.Text = Compress.Bit6Extract(element._compactedData);
}
else if (element._precursor.CompactionCode == (int)CompactionScheme.SevenBitCode)
{
element.Text = Compress.Bit7Extract(element._compactedData);
}
else if (element._precursor.CompactionCode == (int)CompactionScheme.OctectString)
{
element.Text = Encoding.ASCII.GetString(element._compactedData);
}
else if (element._precursor.CompactionCode == (int)CompactionScheme.Utf8String)
{
element.Text = Encoding.UTF8.GetString(element._compactedData);
}
else
{
throw new Exception($"出现意料之外的 CompactScheme {element._precursor.CompactionCode}");
}
}
return(element);
}
// 根据 OID 和字符内容，构造一个 element 的原始数据
// parameters:
// text 内容文字。如果是给 ISIL 类型的, 要明确用 compact_method 指明
// alignment 对齐 block 边界
public static byte[] Compact(int oid,
string text,
CompactionScheme compact_method,
bool alignment)
{
Precursor precursor = new Precursor();
precursor.ObjectIdentifier = oid;
// 自动选定压缩方案
if (compact_method == CompactionScheme.Null)
{
compact_method = Compress.AutoSelectCompressMethod(text);
if (compact_method == CompactionScheme.Null)
{
throw new Exception($"无法为字符串 '{text}' 自动选定压缩方案");
}
}
if (compact_method == CompactionScheme.ISIL)
{
precursor.CompactionCode = (int)CompactionScheme.ApplicationDefined;
}
else
{
precursor.CompactionCode = (int)compact_method;
}
byte[] data = null;
if (compact_method == CompactionScheme.Integer)
{
data = Compress.IntegerCompress(text);
}
else if (compact_method == CompactionScheme.Numeric)
{
data = Compress.NumericCompress(text);
}
else if (compact_method == CompactionScheme.FivebitCode)
{
data = Compress.Bit5Compress(text);
}
else if (compact_method == CompactionScheme.SixBitCode)
{
data = Compress.Bit6Compress(text);
}
else if (compact_method == CompactionScheme.Integer)
{
data = Compress.IntegerCompress(text);
}
else if (compact_method == CompactionScheme.SevenBitCode)
{
data = Compress.Bit7Compress(text);
}
else if (compact_method == CompactionScheme.OctectString)
{
data = Encoding.ASCII.GetBytes(text);
}
else if (compact_method == CompactionScheme.Utf8String)
{
data = Encoding.UTF8.GetBytes(text);
}
else if (compact_method == CompactionScheme.ISIL)
{
data = Compress.IsilCompress(text);
}
else if (compact_method == CompactionScheme.Base64)
{
data = Convert.FromBase64String(text);
}
// 通过 data 计算出是否需要 padding bytes
int total_bytes = 1 // precursor
+ 1 // length of data
+ data.Length; // data
if (precursor.ObjectIdentifier >= 15)
{
total_bytes++; // relative-OID 需要多占一个 byte
}
int paddings = 0;
if ((total_bytes % 4) != 0)
{
paddings = 4 - (total_bytes % 4);
}
// 组装最终数据
List <byte> result = new List <byte>();
// OID 值是否越过 precursor 表达范围
if (precursor.ObjectIdentifier >= 15)
{
precursor.ObjectIdentifier = 0x0f;
}
if (paddings > 0)
{
precursor.Offset = true;
}
result.Add(precursor.ToByte());
if (precursor.ObjectIdentifier == 0x0f)
{
Debug.Assert(oid >= 15);
result.Add((byte)(oid - 15)); // relative-OID
}
// padding length byte
if (paddings > 0)
{
result.Add((byte)(paddings - 1));
}
result.Add((byte)data.Length); // length of data
result.AddRange(data); // data
for (int i = 0; i < paddings - 1; i++)
{
result.Add((byte)0); // padding bytes
}
return(result.ToArray());
}
